A multi-SIM (subscriber identity module) wireless device, including particularly mobile devices such as mobile phones (including so-called “smart phones”), personal digital assistants, tablet and laptop computers, etc., can hold two or more SIM cards. Currently, such devices can typically hold two SIM cards, though phones that can hold three SIM cards are now available and it is likely that phones and other wireless devices that can hold more SIM cards will become available. It is mentioned here that there are proposals to replace SIM cards with SIM functionality provided by software in the device. Reference will be made in this specification generally to “SIM” to mean that part of a device that provides for the subscriber identity module functionality whether provided by a physical card, software elsewhere in the device, or any other suitable arrangement. In addition, for simplicity and brevity, reference will often be made in this specification to a dual-SIM device, which can operate with two networks and/or tariff arrangements, etc., but it will be understood that much of what is described herein can be applied to a multi SIM wireless device having in principle any number of SIMs for operating with a corresponding number of networks and/or tariff arrangements, etc.
Dual-SIM operation allows the use of two services without the need to carry two devices at the same time. For example, the same handset can be used for business and private use with separate numbers and bills. As another example, the same handset can be used for travel, with one SIM being for use in the home country and the other SIM being for the country visited. As another example, both SIMs may be used with the same network operator, for example to achieve a higher total bandwidth for data connections. As yet another example, the device may contain both cellular and non-cellular radios which are used for voice and data communication respectively using the different SIMs. In any event, using multiple SIMs allows the user to take advantage of different pricing plans for calls and text messages to certain destinations as well as mobile data usage, and/or to keep personal and business use separate for example, and/or to achieve higher bandwidth, and/or to obtain coverage across different networks using a single handset. The present invention is particularly concerned with mobile wireless devices that have two (or more) radio systems which can be used simultaneously, and thus allow for example a user to send or receive data whilst making a voice call, and/or to have plural voice calls active simultaneously, and/or to have plural data calls active simultaneously, all on the one device and using the separate radio systems.
With this multiple SIM functionality, the SIMs can in general be from any operator. The carrier frequencies used for communication between the mobile device and the base transceiver station can vary, in effect randomly, depending on the location of the mobile device and what frequencies each service provider has been allocated in that location.
The simultaneously active radio systems can cause radio interference to each other, particularly given that the radio systems are in the same device and physically very close to each other. This is a particular problem when the carrier frequencies used by the two or more SIMS are close to each other. For instance, a GSM (Global System for Mobile Communications) transmission of one radio can use transmission powers above 30 dBm. This can interfere with the reception of another radio, for which the received powers are typically between −50 dBm to −110 dBm, even if different frequencies are being used since some power may leak from the transmit band to the receive band due to the large power difference. Similarly, simultaneous transmission to a far away base station by one SIM radio system uses high power which may interfere with a lower power transmission to a close base station by the other SIM radio system if carriers having similar or close carrier frequencies are used. In general, this problem is exacerbated for a GSM system since 3G (“third generation”) and LTE (“3GPP (3rd Generation Partnership Project) Long Term Evolution”) systems use lower transmission powers over a wider spectrum range. However, a strong GSM carrier can cause interference for other systems as well. This interference problem can also arise from use of non-cellular radios at the same time as the cellular radios on the different SIMs, and indeed generally between radios using many different transmission and reception standards.